The correct option is They are granitic bodies that cool in the deeper depths of the crust..
Explanation
Volcanic landforms are classified into extrusive and intrusive forms based on where the magma cools. Intrusive forms, also known as plutonic landforms, develop when magma cools and solidifies within the Earth's crust before reaching the surface. These forms are exposed on the surface only after prolonged erosion and denudation of the overlying rock layers.
Option Analysis
- They are small surface volcanic domes. is incorrect: Small surface volcanic domes are extrusive features formed by viscous lava piling up over a vent. They are not intrusive bodies.
- They are granitic bodies that cool in the deeper depths of the crust. is correct: Batholiths are large bodies of magmatic material that cool in the deeper depths of the crust. They typically consist of granite and represent the cooled core of massive magma chambers. They develop in the form of large domes and cover extensive areas, often serving as the core of mountain ranges.
- They are horizontal sheets of intrusive rocks. is incorrect: Horizontal sheets of intrusive rocks are known as Sills or Sheets, depending on their thickness. They form when magma solidifies parallel to the bedding planes of sedimentary rocks.
- They are formed by lava cooling on the surface. is incorrect: Landforms created by lava cooling on the surface are classified as extrusive landforms (e.g., lava plateaus, shield volcanoes), not intrusive ones.
Key Takeaway
Batholiths are the largest type of intrusive volcanic landforms, formed by the solidification of granitic magma deep within the crust. They appear on the surface only after the removal of overlying material through erosion.